Indigenous generalist pollinators shape plant-insect interaction networks across a land-use gradient on an oceanic island

Abstract

1. The study asks how plant-pollinator networks reorganise along a land-use gradient spanning five habitat types, ranging from native forests to intensively managed pastures, on the oceanic island of Terceira (Azores, Portugal). 2. Interaction dissimilarity between habitats was always very high (on average 87%) and this reshuffling was driven mainly by plant species turnover rather than insect turnover or partner rewiring. 3. Plant composition shifted strongly along the gradient, with introduced species increasingly dominating disturbed habitats, whereas pollinator richness and identity remained comparatively stable, consistent with more homogeneous communities dominated by widespread generalist indigenous insect species. 4. Connectance and nestedness were lowest, while modularity was highest, in intermediate habitats (naturalized vegetation, exotic forest) a pattern interpreted as the signature of mixed native and introduced floristic pools generating distinct modules, reinforced by locally selective insect foraging. 5. By identifying the species role in the landscape, nearly half of the flower-visiting insects was found to act as habitat connectors linking networks across the gradient. These connectors were mostly indigenous species that behaved as context-dependent generalists, switching plant partners between habitats rather than tracking the same resource everywhere. 6. Widespread pollinators with broad feeding spectra mediated the integration of introduced plants into local pollination networks. This highlights the key role of indigenous super-generalist pollinators in maintaining network resilience across the disturbance gradient. Nevertheless, the reliance on a few super-generalist species for pollination across diverse habitat-types, as reported from several archipelagos worldwide, pinpoints the vulnerability of these ecosystems to pollinator declines.